Cable with air insulation



Jan. 2, 1951 J BEUCKENS ETAL (ABLE WITH AIR INSULATION Filed June 24, 1946 I N V EN TORS. c//l COBUS BEUCIQNS BY EI TRTARIJ JAN )VIOL Patented Jan. 2, 1951 CABLE WITH AIR INSULATION Jacobns Beuckcns and Evert Arij Jan Mol, Venlo, Netherlands, assignors, by mesne assignments, to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application June 24, 1946, Serial No. 678,780 In the Netherlands January 23, 1942 Section 1, Public Law 690, August 8, 1946 Patent expires January 23, 1962 3 Claims. 1

The invention relates to cables wherein in connection with their use low dielectric losses and, in addition, a slight mutual capacity between the conductors present therein or a slight capacity between these conductors and an external conductive envelope is desired, such as cables for carrier-wave telephony, for television, for aerials and other purposes.

In order to maintain the said capacity at a low value it has been proposed to constitute the insulation in such cables partly by air. In this connection cables with air insulation wherein use is made of a helically wound thread or ribbon of paper are well-known. Due to the harmful properties of paper, more particularly to the high sensitivity to moisture, these cables exhibit high dielectric losses unless particular precautions against the penetration of moisture are taken, for example by providing a lead sheath.

An appreciable improvement in these respects has been obtained by replacing paper by polystyrene or similar polymerides of arylolefines. In contrast with paper these substances exhibit, however, more particularly at temperatures below C., a great brittleness, which is harmful in the use in cables. This brittleness, which reduces the flexibility of the cables, exists when a thread or ribbon of polystyrene is he.ically wound although in this case the cables are substantially not under strain of bending but are under strain of torsion.

It is 'true that for removing the said drawback it would be possible to utilize the polystyrene in drawn-out condition but at the low temperatures above referred to th s does not reduce the brittleness to an appreciable extent.

It has been found that air-insulated cables of satisfactory flexibility, even at low temperatures, may be obtained by utilizing helically wound threads or ribbons consisting of polyvinylchloride or similar polymerides containing chlorine, such as chlorinated polyvinylchloride and mixed polymerisates on the basis of polyvinylchloride, which contain a softener in so low a percentage that the dielectric losses are lower than about 100 10- measured at a wavelength of from 50 to 200 meters at room temperature. The softeners commonly utilized with the said insulating materia's, such as tricresylphosphate, chlorinated diphenyl, dibutylphthalate and the like enter into account for carrying the invention into effect.

The thread or ribbon may be utilized either solid or hollow or properly profiled and, if de-- sired, provided with inlaid portions either conductive or not. J

With the said dielectric losses sufllciently low for practical appliances the insulation according to the invention is to a high extent resistant to compressive strain and insensitive to moisture.

As appears from the above, the invention is based on the recognition that by utilizing a suitable percentage of the softener it is possible to obtain in a simple manner the said combination of favourable properties. Within the scope of the invention the required percentage of the softener is slightly dependent upon the nature of the polymerisate and of the softener utilized therewith. The upper limit thereof is determined by the requirement about the dielectric losses and the lower limit by the required flexibility, a content of at least about 10% being generally required therefor.

With the cables according to the invention it is further important that the insulation should be non-inflammable and resistant against the effect of light and atmospheric influences. A further advantage is that the insulation is substantially not attacked by aliphatic hydro-carbides, which is important for example in the use as a cable for a motorcar aerial.

The insulation according to the invention may be utilized in bare conductors as .well as in con ductors already provided with an insulating layer while the conductors may be located therein so as to be entirely free or may be locally supported. The heically wound insulation is preferably surrounded by a flexible insulating sheath, for example in the form of foil, which may be surrounded by an external conductive layer which acts as an electric screen, for example by a metal covering or a conductive layer of varnish, which, if desired, may be surrounded in its turn, for ex ample, by a cotton covering.

The invention will be explained more fully with reference to the accompanying drawing.

In this drawing l denotes a copper wire having a. diameter of 0.25 mm., which wire is located freely within a helically wound thread 2 with a thickness of 1.2 mm. which consists of polyvinylchloride which has been plastifled with 15% of diphenylchloride, the thread of polyvinylchloride being wound during this operation on a mandrel of 5 mms. with a pitch of 4 mms. Then there has been proviedd a covering of polyvinylchloride foil 3 which is surrounded successively by a metal covering 4, which acts as a screen, and by a cotton covering 5.

What we claim is:

aeaaeoa 1. An air-insulated flexible cable comprising a tubular flexible insulating sheath, a conductor *element freely disposed within said sheath, and

a helically wound ribbon of insulating material within said sheath, said insulating material comprising a chlorinated polymeride and between apbient temperature.

2. An air-insulated flexible cable comprising a tubular flexible insulating sheath, a conductor element freely disposed within said sheath, and a helically wound ribbon of insulating material within said sheath, said insulating material comprising polyvinyl chloride and about 15% of diphenyl hloride, said insulating material having dielectr e losses less than about 100 1O at wavelengths between'50 and 200 meters measured at the ambient temperature.

3. An air-insulated flexible cable comprising a tubular flexible insulating sheath, a conductive layer on the outer surface of said tubular sheath, a conductor element freely disposed within said sheath, and a helically wound ribbon of insulating material within said sheath. said insulatin material comprising a chlorinated polymeride and a plasticizer in an amount between 10 and 15% of the insulating material, said insulating material having dielectric losses less than about 100x10- at wavelengths between 50 and 206 meters measured at the ambient temperature.

JACOBUS BEUCKENS.

EVmT ARIJ JAN MOI...

REFERENCES @FEEHD The following references are of record in the file of this patent:

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